Chevron Corp. drilled 84 wells to a depth of two miles beneath the Indonesian rainforest to tap steam, not oil and gas, that's trapped in the world's richest store of volcanic energy.

The geothermal plant, set among wild orchids and bamboo trees, uses 315 degree Celsius (600 degree Fahrenheit) heat to spin turbines 24 hours a day, generating electricity for Jakarta, a four-hour drive to the north. The oil driller, which pioneered geothermal energy 20 years ago in Southeast Asia's biggest economy, is about to see competition.

Companies from General Electric Co. to India's Tata Corp. are leading an investment boom in Indonesia that may climb to more than $30 billion, anticipating President Susilo Bambang Yudhoyono will honor his promise in February to boost clean- energy subsidies. The pledge has spurred the biggest geothermal spending spree in Asia and the largest outside of the U.S.